Many industrial practices require a succession of articles being processed to be turned to change the orientation of the articles, for example, to lie each article on its side or to invert the article, and in the container and packaging industries an open rigid container may be turned a number of times between manufacture and the final charging and closure of the container.
There are a number of powered devices for turning articles but such powered devices are complicated and expensive to manufacture, requiring a continuous power supply and are therefore expensive to run and maintain, and as such devices normally run at a constant speed they cannot readily accommodate surges in the production line.
It is also well known in the art to use static turning devices for turning articles and such devices conventionally comprise continuously fixed guide surfaces inclined to the general direction of displacement of the articles so that, as each article is advanced along said guide surfaces whilst maintaining its general direction of displacement, the article is continuously turned about an axis parallel to its general direction of displacement. To maintain control of the articles passing through the static turning device, thus to prevent an article from tipping forwardly or rearwardly relative to the general direction of displacement, and to provide the force for driving the articles through the device, the articles are supplied to, and pass through, the device with each article contacting the adjacent preceding and succeeding article and the driving force is applied through the articles waiting to enter the device and is transmitted to the articles in the device by the contacting relationship of the articles.
In one well known and recognised method for developing the driving force to urge articles through the turning device articles to be turned are delivered to the device on a conveyor which runs faster than the rate of displacement of articles through the device, this allows an accumulation of articles, in succession, on the conveyor and the frictional engagement of the articles with the conveyor develops the driving force necessary to drive the articles through the device.
Articles capable of being turned by the turning device must have sufficient rigidity to receive and transmit the driving force, to withstand the substantial forces developed between the article and the inclined guide surfaces, and sufficient rigidity for the article to be turned by the guide surfaces and any article having the rigidity to meet those parameters is a "substantially rigid" article as that term is used in the present specification.
It will be appreciated that each guide surface effective on an article must follow a spiral path around the axis of the device and the device must be capable of withstanding thrust exerted on the guide surfaces by the turning articles acting under the driving force and to meet these requirements the inclined guide surfaces are conventionally formed on elements of substantial mass extending in the direction of the device and the working of the spiral guide surfaces on said elements is a complicated and very expensive exercise.